This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The animals were immunized with a vaccine composed of HIV proteins, gp120 and nef/tat, and SIV nef protein administered along with various proprietary adjuvants. After three immunizations, the animals were challenged intravenously with SHIV89.6P in 1999. This experiment was transferred to the SVEU at the WaNPRC by NIAID in 2001. SVEU support continues through the current year. The surviving animals are long-term nonprogressors who are controlling virus replication, maintaining very low or undetectable virus levels. Samples are collected from them as requested by the home laboratory or the SVEU project officer to monitor the persistence of immune responses elicited by the vaccine and challenge and as needed for health monitoring. Additionally, blood from these animals is being collected to validate new intracellular staining assays to be used to evaluate cellular immunity developed in response to vaccines being studied on this as well as other projects supported by the SVEU contract. Before the end of this reporting period, in an effort to better understand the mechanisms of virus control by vaccines, we plan to examine the role of CD8+ cells in controlling virus in these animals by temporarily depleting CD8+ cells in vivo by treatment with the humanized mouse monoclonal anti-CD8 antibody, cM-T807.